The invention relates to a triggering mechanism for a safety device in a vehicle, in particular for a side airbag. The triggering device has a deformation sensor which is made up of at least one pressure-sensitive sensor element. The triggering mechanism is arranged directly under the outer skin of the vehicle and, in the event of a collision-induced deformation of the outer skin, electric deformation signals are emitted to an evaluation circuit. The evaluation circuit determines a rate of deformation in order to trigger the safety device if a threshold value is exceeded.
Passive safety devices, which in the event of an accident are triggered without any action on the part of the vehicle occupants, have long been known. For example, the airbag system which by now is standard equipment in most motor vehicles, automatically inflates an air cushion in the steering wheel or dashboard in the event of a frontal collision of the vehicle against an obstacle in order to protect the occupants against head injuries.
In order to improve protection also in the event of a side collision of the vehicle, it is possible to arrange airbag systems in the side region of the vehicle. Since there are only minimal crash zones which absorb part of the collision energy in the side region, the time period available to bring a side airbag into a state which affords effective protection is very much smaller than in the case of a frontal collision. Therefore, high requirements for a quick and reliable response are demanded of a deformation sensor and an evaluation circuit for detecting a side collision. However, unnecessary triggering of the safety device is also to be avoided if the occupants are not endangered, for example, if when parking an obstacle very slowly deforms the outer skin of the vehicle. Therefore, it is also advisable to measure the rate at which the outer skin is deformed.
A triggering mechanism having a deformation sensor for determining a rate of deformation is generally known from German Patent document 3,716,168. The deformation sensor is arranged directly underneath the outer skin in the side region of the vehicle and extends over the entire width of a door. The deformation sensor is made up of two sensor elements arranged one behind the other at a small distance. As soon as the outer skin is deformed by an external force, the sensor elements respond, one after the other, and emit electric signals to an evaluation circuit. With a given spatial distance between the two sensor elements, the time interval between the two signals depends solely on the rate at which an obstacle deforms the skin, i.e., pushes into the vehicle. To a limited extent, this measure of the rate of deformation can be used to reach a conclusion as to the impending danger to the occupants. If a critical rate is exceeded, therefore, the safety device is triggered. The evaluation circuit checks the time sequence of the emitted signals and, if the sequence is correct and other preconditions regarding strength and duration are satisfied, triggers the safety device. Provided as sensor elements are light guides which give off a signal in the event of a malfunction. A further exemplary embodiment provides pressure sensors in the bearings of structural elements in the side region of the vehicle, for example, reinforcing tubes.
A disadvantage of the known deformation sensor is that its installation and exchange, for example if the sensing hardware is defective, requires considerable expenditures. The known arrangement also requires the first sensor element to be destroyed or badly damaged before the second sensor element ever responds. The first sensor element will also be destroyed or badly damaged even for the eventuality that the deformation is slow and is not assessed as critical in terms of safety by the evaluation circuit. Therefore, registration of a slight collision, which is virtually non-destructive for the deformation sensor, is rarely possible and thus causes increased repair costs.
There is therefore needed a deformation sensor which is inexpensive, avoids the disadvantages of the known deformation sensor, and can largely exclude the possibility of the safety device being inadvertently triggered.
These needs are met according to the present invention by a trigger mechanism for a safety device in a vehicle, in particular for a side airbag. The triggering device has a deformation sensor which is made up of at least one pressure-sensitive sensor element. The triggering mechanism is arranged directly under the outer skin of the vehicle and, in the event of a collision-induced deformation of the outer skin, electric deformation signals are emitted to an evaluation circuit. The evaluation circuit determines a rate of deformation in order to trigger the safety device if a threshold value is exceeded. At least one sensor element is attached on a fixed carrier plate, parallel to the outer skin. Spacer elements support the carrier plate against a structural element in the vehicle running parallel to the outer skin so that, in the event of an outer force effect on the outer skin, a first reliable response of the sensor element, facing the outer skin with its pressure-sensitive side, is ensured. The spacer elements yield if the force effect increases further above a defined threshold, in such a way that the carrier plate is brought against the structural element, so that, upon striking the structural element, a second sensor signal is emitted.
An advantage of the deformation sensor according to the present invention is that a collision-induced force effect on the first sensor element is passed on by the common carrier plate to the spacer element. The spacer elements, which form a certain threshold, yield to the pressure until the carrier plate or the second sensor element strikes the member. By virtue of the threshold-like response characteristic, which follows the yielding of the spacer elements to an external pressure, a defined, clear response behavior of the deformation sensor is achieved. The design of the deformation sensor according to the present invention with clip elements for clip ping onto the member also offers the advantage of a simple attachment underneath the outer skin.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.